1. Field of the Invention
The present invention relates to a fuel supply device of a motorcycle.
2. Related Art
In a recent method of supplying fuel to an engine using a fuel injector, it is necessary for a motorcycle to be equipped with a fuel pump. In an example of installation place and installation method of the fuel pump include, a fuel pump is mounted on the upper surface of a crankcase behind a cylinder (as shown in Japanese Patent Laid-Open Publication No. 2005-096504), a fuel pump is housed inside of a side portion of a fuel tank having a horseshoe section straddling a frame pipe (as shown in Japanese Patent Laid-Open Publication No. 2007-015468), or a fuel pump is inserted from a upper side of a fuel tank (as shown in Japanese Patent Laid-Open Publication No. 2005-170273).
However, in a case where the fuel pump is mounted on the upper surface of a crankcase behind the cylinder, the fuel tank is disposed above the cylinder, and thus, a fuel pipe extending from the fuel tank to a fuel pump and a fuel pipe extending from the fuel pump to a fuel injector have long length. Therefore, it is required for a fuel pump to have a high discharging performance. Moreover, since an exhaust pipe exists near the fuel pipe, there is a possibility that percolation may occur, which is not preferable and disadvantageous.
On the other hand, in a case where a fuel pump is housed in one side of the fuel tank, the fuel pump can be housed only by disposing the fuel pump close to the front portion of the fuel tank because the fuel pump is relatively high, and the fuel pump is disposed far from an injector. As a result, the fuel pipe is made long, and a fuel pump having a high exhaust performance is hence required, which is not preferable.
Further, the side portion of the fuel tank needs a height dimension enough to house the fuel pump, and thus, it becomes necessary to lower a lower edge of the fuel tank or to set high a frame pipe. In the former case, since the engine mounting position becomes lower, a sufficient minimum road clearance cannot be secured. In the latter case, conversely, the position of the fuel tank is made high and then, the gravity center also becomes high. This leads to distribution of mass, and therefore, the vehicle body gravity center is not well balanced.
Furthermore, in the case of a mounting structure in which the fuel pump is inserted from the upper surface of the fuel tank, the fuel pipe is made long, and it is hence required for a fuel pump to have a high discharge performance. Further, since influence of fuel pipe deflection or expansion is intensified, still higher discharge performance is required, which is not preferable.